1. Field of the Invention
This invention relates to a shutter mechanism for a camera. This invention particularly relates to a shutter mechanism for a camera provided with a zoom lens, wherein a lens aperture on a wide side is restricted.
2. Description of the Related Art
In cases where wide angle photographing (i.e., wide side photographing) is performed with cameras provided with zoom lenses, besides rays having small angles of deflection with respect to an optical axis of the lens, the rays having large angles of deflection with respect to the optical axis of the lens also impinge upon the lens. Therefore, in such cases, aberration becomes larger than in the cases of telescopic photographing (i.e., zoom side photographing), and a marginal blur becomes apt to occur with the obtained image. Accordingly, in cases where the wide angle photographing is performed, ordinarily, a shutter aperture is stopped down, such that the rays having large angles of deflection may be blocked, and an image having good image quality and free from a blur at the marginal area may be obtained.
As a mechanism for stopping down the lens aperture, an aperture opening restricting device disclosed in, for example, Japanese Unexamined Patent Publication No. 2000-235209 has heretofore been known. The disclosed aperture opening restricting device is provided with a restricting member for coming into abutment with shutter blades immediately before the shutter blades reach the positions for full opening of the lens aperture during opening movements of the shutter blades, and thereby obstructing further opening movements of the shutter blades. The restricting member is an approximately L-shaped member and has a restriction pin-at one end of the L-shaped member. When the shutter blades perform the opening movements, the restriction pin enters into the movement loci of the shutter blades, comes into abutment with the shutter blades, and thereby stops the shutter blades. The restricting member has its rotation center at a corner area of the L-shaped member, and the other end side of the restricting member takes on the form of a projecting member. The projecting member comes into abutment with a cam, which is formed in a slant state on an internal surface of a cam cylinder. The position of the restriction pin for obstructing the opening movements of the shutter blades is determined by the position, at which the cam and the projecting member abut against each other.
With the aperture opening restricting device described above, the degree of opening of the lens aperture is determined by the position, at which the projecting member and the cam engage with each other. Therefore, the problems may often occur in that the degree of opening of the lens aperture vary for different photographing operations due to a slight shift of the position, at which the projecting member and the cam engage with each other. Therefore, there is the risk that the image quality of the obtained image will fluctuate. Also, there is a distance between the restriction pin and the position, at which the projecting member and the cam engage with each other, and therefore there is the risk that the position of the restriction pin will become indefinite due to fitting looseness of the restricting member, or the like.
The primary object of the present invention is to provide a shutter mechanism for a camera, wherein a predetermined lens aperture diameter is capable of being obtained reliably.
The present invention provides a shutter mechanism for a camera, comprising:
i) a lens shutter constituted of a plurality of shutter blades, which are capable of being moved within a shutter chamber of a camera in order to open and close a lens aperture, and
ii) a stopper, which is capable of entering into movement loci of the shutter blades, the stopper selectively taking a position for aperture restriction that stops the shutter blades immediately before the shutter blades reach positions for full opening of the lens aperture during opening movements of the shutter blades, or a position for restriction release that allows the shutter blades to reach the positions for the full opening of the lens aperture,
wherein the stopper is urged by a spring toward the position for the aperture restriction, and
the stopper is retracted by stopper releasing means to the position for the restriction release in cases where the lens aperture is to be fully opened.
The shutter mechanism for a camera in accordance with the present invention may be modified such that the stopper is a lever for rotation around a supporting point, which lever is provided with a stopping section that stops the shutter blades, and
the lever is urged by the spring such that the stopping section of the lever is ordinarily in abutment with an abutment surface, which is formed on the side of a wall member constituting the shutter chamber and is located at a predetermined position within the movement loci of the shutter blades.
Also, in such cases, the shutter mechanism for a camera in accordance with the present invention may be modified such that the lever is provided with a section-to-be-pushed, which is formed on the side opposite to the stopping section with the supporting point of the lever intervening between the section-to-be-pushed and the stopping section, and
the section-to-be-pushed is adapted to be pushed by the stopper releasing means such that the stopping section is retracted to the position for the restriction release.
Further, the shutter mechanism for a camera in accordance with the present invention may be modified such that a lever engagement member is associated with the wall member constituting the shutter chamber, such that the position of the lever engagement member is capable of being adjusted in a direction heading towards the stopping section of the lever and in a direction heading away from the stopping section of the lever, and
the abutment surface is formed on the lever engagement member.
With the shutter mechanism for a camera in accordance with the present invention, the stopper, which is capable of entering into the movement loci of the shutter blades in order to obstruct the opening movements of the shutter blades, is urged by the spring toward the position for the aperture restriction. In cases where the lens aperture is to be fully opened, the stopper is retracted by the stopper releasing means to the position for the restriction release. Therefore, the position for the aperture restriction, which the stopper takes, is kept at the predetermined position. Accordingly, a predetermined lens aperture diameter is capable of being obtained reliably.
With the shutter mechanism for a camera in accordance with the present invention, the stopper may be the lever for rotation around the supporting point, which lever is provided with the stopping section that stops the shutter blades, and the lever may be urged by the spring such that the stopping section of the lever is ordinarily in abutment with the abutment surface, which is formed on the side of the wall member constituting the shutter chamber and is located at the predetermined position within the movement loci of the shutter blades. In such cases, with the simple constitution, the position for the aperture restriction, which the stopper takes, is capable of being kept at the predetermined position, and the predetermined lens aperture diameter is capable of being obtained reliably.
Also, with the shutter mechanism for a camera in accordance with the present invention, the lever may be provided with the section-to-be-pushed, which is formed on the side opposite to the stopping section with the supporting point of the lever intervening between the section-to-be-pushed and the stopping section, and the section-to-be-pushed may be pushed by the stopper releasing means such that the stopping section is retracted to the position for the restriction release. In such cases, the accurate restriction of the lens aperture and the full opening of the lens aperture are capable of being achieved with the simple constitution.
Further, with the shutter mechanism for a camera in accordance with the present invention, the abutment surface maybe formed on the lever engagement member, which is associated with the wall member constituting the shutter chamber, such that the position of the lever engagement member is capable of being adjusted in the direction heading towards the stopping section of the lever and in the direction heading away from the stopping section of the lever. In such cases, the position of the stopping section of the stopper is capable of being altered.
Therefore, regardless of fluctuation in accuracy of products (or parts), the accurate exposure opening degree, i.e. the accurate lens aperture diameter, is capable of being set reliably at the stage of camera production.